From here you can grab the driver version associated with your version of ESXi: http://partnerweb.vmware.com/comp_guide2/detail.php?deviceCategory=io&productid=36026&vcl=true

Then check to make sure your build matches the associated version of the driver you want: http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1014508

You can then install them in:
ESXi 5.x: http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=2005205#offlinewithzip
ESXi 4.x: http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1032936